#define _CRT_SECURE_NO_WARNINGS 1
#include <iostream>

class Solution {
public:
    int sumNumbers(TreeNode* root)
    {
        return dfs(root, 0);
    }
    int dfs(TreeNode* root, int presum)
    {
        presum = presum * 10 + root->val;

        if (root->left == nullptr && root->right == nullptr) return presum;
        int ret = 0;
        if (root->left) ret += dfs(root->left, presum);
        if (root->right) ret += dfs(root->right, presum);

        return ret;
    }
};